In cases of SCD the biological properties of NO, such as regulation of vascular tone and/or aggregation and adhesion in the vascular compartment, are impaired, due to the reduced bioavailability of the gas [46,47]; moreover, given the high presence of HbS, NO reacts with the protein leading to the formation of a very stable complex, Fe2+Hb-NO, which can potentially be involved in the Fenton reaction [48]. Here, GSTM1 is linked to Schnyder corneal dystrophy.